Towards the Application of Weak Base and Chelation Ion Exchange Resins for the Development of a Sustainable Uranium Recovery Process

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Abstract

The current low uranium spot price and an increased awareness of environmental sustainability issues are driving the need for innovation within the uranium mining industry. A key area of interest is the use of lower quality waters in uranium processing circuits. These lower quality waters contain many species generally viewed as contaminants in processing flowsheets, such as Cl- and Fe3+, the presence of which will greatly reduce the ability of conventional processing technologies to function efficiently, in particular, ion exchange (IX) columns. The most common IX resins used in uranium processing flowsheets are strong base anion exchange resins, and suffer from supressed uptake in high [Cl-] environments and are not selective for UO22+ over Fe3+. It has been shown that other types of IX resin, namely weakly basic anion (WBA) exchange resins and chelation ion exchange resins, may be capable of overcoming these problems. A series of weak base anion (WBA) exchange resins have been synthesised and characterised via elemental analysis, thermogravimetric analysis, infra-red spectroscopy and solid state carbon-13 nuclear magnetic resonance spectroscopy. Extended X-ray absorption fine structure (EXAFS) spectroscopy has determined uranyl coordination environment on the synthesised resins, Dowex M4195, Purolite S985, Purolite S930+, Purolite S957 and Purolite S910, when extracting from non-saline and saline ([Cl-] = 22.6 g L-1) environments. This has been used to understand uranyl extraction mechanism. The synthesised resins and Purolite S985 are reported to not extract multiple aqueous ionic species from sulfuric acid media. Increasing [Cl-] causes a decrease in uranyl recovery, but tolerance is greater than that of SBA resins. Uranyl uptake is moderately suppressed in mixed Fe-U systems, and the presence of UO22+ promotes Fe3+ extraction. Chelation resin Purolite S930+ shows a dependence on [H+] with regards to UO22+ recovery from both H2SO4 and HCl media. Increasing [Cl-] does not affect recovery, whereas increasing [SO42-] (> 1 M) causes suppression of up to 15%. Systems where [Fe3+]/[UO22+] = 2 show 66% less recovery than pure uranyl sulfate solutions. Synthesised WBA resin Ps-EDA (ethylenediamine) shows a dynamic maximum loading capacity of 98.27 mg g-1. No effect of Cl- is seen up to 5 g L-1, however, above 20 g L-1 not uranyl loading is observed. Breakthrough behaviour with varying flow rate and [Cl-] are most adequately predicted by the Modified Dose-Response model.

Keyword(s)

Chelation; Ion Exchange; Mining; Saline; Uranium; Weak Base

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